Cathodic electrosynthesis of iron oxide films for electrochemical supercapacitors

Cathodic electrosynthesis has been utilized for the fabrication of γ-Fe₂O₃ films, containing chitosan additive as a binder. The films were studied by X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, differential thermal analysis, and thermogravimetric analysis. Cyclic voltammetry and chronopotentiometry data showed that the iron oxide films exhibit electrochemical capacitance in the voltage window of −0.9 to −0.1 V vs SCE in 0.25 m Na₂SO₄ and 0.25 m Na₂S₂O₃ aqueous solutions. The highest specific capacitance (SC) of 210 F g⁻¹ was achieved using 0.25 m Na₂S₂O₃ as electrolyte, at a scan rate of 2 mV s⁻¹. The SC decreased with increasing film thickness, scan rate and cycle number. Heat treatment of the films at 140 °C resulted in increasing SC.     

Kinetics and mechanism of the electrochemical reduction of molecular oxygen on platinum in KOH: influence of preferred crystallographic orientation

The oxygen electroreduction reaction has been studied at both preferred oriented and conventional polycrystalline platinum rotating disc electrodes in x m KOH (0.05 ⩽ x ⩽ 3.0) aqueous solutions under oxygen saturation at 25°C. At low current densities, Tafel lines with slope -0.060 V decade⁻¹ have been obtained at all platinum electrodes. At high current densities, higher Tafel slopes ranging from -0.18 to -0.40 V decade⁻¹ have been observed, depending on the type of preferred oriented Pt and KOH concentration. Rotating ring-disc electrode data have shown that a higher amount of H₂O₂ is produced on one type of preferred oriented surface at all KOH concentrations. A complex reaction scheme has been used to evaluate the electrochemical rate constants of the reaction steps at three platinum electrodes.     

The Allelochemical L-DOPA Increases Melanin Production and Reduces Reactive Oxygen Species in Soybean Roots

The non-protein amino acid, L-3,4-dihydroxyphenylalanine (L-DOPA), is the main allelochemical released from the roots of velvetbean and affects seed germination and root growth of several plant species. In the work presented here, we evaluated, in soybean roots, the effects of L-DOPA on the following: polyphenol oxidase (PPO), superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities; superoxide anion ( \textO₂^·- ) \left( {{\text{O}}_2^{{\bullet - }}} \right) , hydrogen peroxide (H₂O₂), and melanin contents; and lipid peroxidation. To this end, 3-day-old seedlings were cultivated in half-strength Hoagland’s solution (pH 6.0), with or without 0.1 to 1.0 mM L-DOPA in a growth chamber (at 25°C, with a light/dark photoperiod of 12/12 hr and a photon flux density of 280 μmol m⁻² s⁻¹) for 24 hr. The results showed that L-DOPA increased the PPO activity and, further, the melanin content. The activities of SOD and POD increased, but CAT activity decreased after the chemical exposure. The contents of reactive oxygen species (ROS), such as \textO₂^·- {\text{O}}_2^{{\bullet - }} and H₂O₂, and the levels of lipid peroxidation significantly decreased under all concentrations of L-DOPA tested. These results suggest that L-DOPA was absorbed by the soybean roots and metabolized to melanin. It was concluded that the reduction in the \textO₂^·- {\text{O}}_2^{{\bullet - }} and H₂O₂ contents and lipid peroxidation in soybean roots was due to the enhanced SOD and POD activities and thus a possible antioxidant role of L-DOPA.     

Characterisation of a laboratory electrochemical ozonation system and its application in advanced oxidation processes

An electrochemical reactor for oxygen/ozone production was developed using perforated planar electrodes. An electroformed -PbO₂ coating, deposited on a platinised titanium substrate, was employed as anode while the cathode was a platinised titanium substrate. The electrodes were pressed against a solid polymer electrolyte to minimise ohmic drop and avoid mixing of the gaseous products (H₂ and O₂/O₃). Electrochemical ozone production (EOP) was investigated as function of current density, temperature and electrolyte composition. Electrochemical characterisation demonstrated ozone current efficiency, Φ_EOP, ozone production rate (g h⁻¹), , and grams of O₃ per total energy demand (g h⁻¹ W⁻¹), increase on decreasing electrolyte temperature and increasing current density. The best reactor performance for EOP was obtained with the base electrolyte (H₂SO₄ 3.0 mol dm⁻³) containing 0.03 mol dm⁻³ KPF₆. Degradation of reactive dyes used in the textile industry (Reactive Yellow 143 and Reactive Blue 264) with electrochemically-generated ozone was investigated in alkaline medium as function of ozone load (mg h⁻¹) and ozonation time. This investigation revealed ozonation presents very good efficiency for both solution decolouration and total organic carbon (TOC) removal.     

Development of a new biosensor for mediatorless voltammetric determination of hydrogen peroxide and its application in milk samples

A new biosensor for the voltammetric detection of hydrogen peroxide was developed based on immobilization of catalase on a clinoptilolite modified carbon paste electrode using bovine serum albumin and glutaraldehyde. The biosensor response was evaluated according to electrode composition, reaction time, solution pH and temperature. The voltammetric signals were linearly in proportion to H₂O₂ concentration in the range 5.0 × 10⁻⁶–1.0 × 10⁻³ M with a correlation coefficient of 0.9975. The detection limit is 8.0 × 10⁻⁷ M and the relative standard deviation for 4.0 × 10⁻⁴ M hydrogen peroxide was 1.83% (n = 6). The biosensor exhibited high sensitivity, and it was determined that it could be used for more than 2 months. In addition, the biosensor was successfully applied for the determination of hydrogen peroxide in milk samples.     

Sol-gel derived carbon ceramic electrode for the investigation of the electrochemical behavior and electrocatalytic activity of neodymium hexacyanoferrate

The electrochemical properties of an electroactive rare earth metal hexacyanoferrate, neodymium hexacyanoferrate (NdHCF) were studied by mechanically attaching NdHCF samples to the surface of carbon ceramic electrodes (CCEs) derived from sol-gel technique. The resulting modified electrodes exhibit well-defined redox responses with the formal potential of 0.241 V (versus SCE) at a scan rate of 20 mV s⁻¹ in 0.5 M KCl solution. The voltammetric characteristics of the NdHCF-modified CCEs in the presence of different alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) were investigated by voltammetry. The NdHCF-modified CCEs presented a good electrocatalytic activity towards the reduction of hydrogen peroxide (H₂O₂), and was used for amperometric detection of H₂O₂. In addition, the NdHCF-CCEs exhibited a distinct advantage of simple preparation, surface renewal, good stability and reproducibility.     

The O<Subscript>2</Subscript> + NH<Subscript>3</Subscript> Reaction Over Rh(110): Steady State Kinetics and Oscillatory Behavior

Abstract  

The kinetics of ammonia oxidation with oxygen over a Rh(110) surface were studied in the pressure range 10⁻⁵–10⁻⁴ mbar. Nitrogen was found to be the preferred product at low partial pressures ratios \textp_{\texto 2} :\textp_{\textNH 3} {\text{p}}_{{{\text{o}}_{ 2} }} :{\text{p}}_{{{\text{NH}}_{ 3} }} , while the NO pathway was favored with oxygen rich gas mixtures and at high temperature. The reactive sticking coefficient of O₂ reaches up to 0.05 under steady state conditions. Pronounced hysteresis effects in the reaction rates were found in T-cycling experiments. Sustained oscillations in the reaction rates occurred under isothermal conditions at T = 620 K at a total pressure of 4 × 10⁻⁵ mbar.     

Intrinsic viscosity-number average molecular weight relationship for poly (n-Octadecyl acrylate) and poly (N-n-octadecylacrylamide)

Intrinsic viscosity-number average molecular weight relationships have been measured, at 30C in benzene, for poly (n-octadecyl acrylate) as [η]=2.72×10⁻⁴ Mn^0.638 and for poly (N-n-octadecylacrylamide) as [η]=0.82×10⁻⁴ Mn^0.676. Whole polymers of various molecular weights were prepared in benzene solution at 65C with dodecyl mercaptan as primary regulator. By the use of these parameters, the molecular weight of such polymers and their homologs may now be measured by simple solution-viscosity determinations. In the expression { } (relating degrees of polymerization { } to the mercaptan/monomer ratio), intercept { } and apparent transfer constant C_s for n-octadecyl acrylate were 6.28×10⁻³ and 0.68; for N-n-octadecylacrylamide 1.10×10⁻³ and 0.62 respectively. These parameters permit preparation of homopolymers of chosen molecular weight. Presented at the AOCS Meeting, Philadelphia, October 1966 E. Utiliz. Res. Devel. Div., ARS, USDA.     

Heterogeneous photocatalytic reduction of Fe(VI) in UV-irradiated titania suspensions: effect of ammonia

Results of the heterogeneous photocatalytic reduction of Fe(VI) in UV-irradiated TiO₂ suspensions in the presence of ammonia are presented. The initial rate of Fe(VI) reduction, R, may be expressed as R = k _Fe(VI)[Fe(VI)]^1.25 where k _Fe(VI) = a[Ammonia]+b), a = 6.0 × 10³ μm ^0.25 s and b = 4.1 × 10⁶ μm ^−1.25s⁻¹. The rate constant, k _Fe(VI), increases with the ammonia concentration. The photocatalytic oxidation of ammonia is enhanced in the presence of Fe(VI). A mechanism involving Fe(V) as a reactive intermediate is presented which explains the faster photocatalytic oxidation of ammonia in the presence of Fe(VI).     

Two New Organic–Inorganic Hybrids Based on [SiW12O40]4? Anion: Hydrothermal Syntheses, Crystal Structures, and Electrochemical Properties

Two new organic–inorganic hybrid compounds [\textCu^\textI ( \texten ) ₂ ( \textH ₂ \textO )] ₂ { ( \textSiW^\textVI _{1 1} \textW^\textV ₁\textO ₄₀ ) ₂ [ \textCu^\textII ( \texten ) ₂ ( \textH ₂ \textO )] ₂ [\textCu^\textII ( \texten ) ₂ ] ₂ }·6 \textH ₂ \textO [{\text{Cu}}^{\text{I}} \left( {\text{en}} \right)_{ 2} \left( {{\text{H}}_{ 2} {\text{O}}} \right)]_{ 2} \left\{ {\left( {{\text{SiW}}^{\text{VI}}_{ 1 1} {\text{W}}^{\text{V}}_{ 1}{\text{O}}_{ 40} } \right)_{ 2} \left[ {{\text{Cu}}^{\text{II}} \left( {\text{en}} \right)_{ 2} \left( {{\text{H}}_{ 2} {\text{O}}} \right)\left] {_{ 2} } \right[{\text{Cu}}^{\text{II}} \left( {\text{en}} \right)_{ 2} } \right]_{ 2} } \right\}{\cdot}6 {\text{H}}_{ 2} {\text{O}} (1) and (H₂ L)₂[SiW₁₂O₄₀]·H₂O (2) [en = ethylenediamine, L = 1,4-bis(3-pyridinecarboxamido)benzene], have been hydrothermally synthesized and characterized by IR, elemental analyses, TG analysis, and single-crystal X-ray diffraction. Structural analyses indicate that compound 1 exhibits an interesting three-dimensional(3D) cross-like supramolecular network through arrangement of a 1D organic–inorganic hybrid chain { ( \textSiW^\textVI _{1 1} \textW^\textV ₁ \textO ₄₀ ) ₂ [ \textCu^\textII ( \texten ) ₂ ( \textH ₂ \textO )] ₂ [\textCu^\textII ( \texten ) ₂ ] ₂ } ^2- . \left\{ {\left( {{\text{SiW}}^{\text{VI}}_{ 1 1} {\text{W}}^{\text{V}}_{ 1} {\text{O}}_{ 40} } \right)_{ 2} \left[ {{\text{Cu}}^{\text{II}} \left( {\text{en}} \right)_{ 2} \left( {{\text{H}}_{ 2} {\text{O}}} \right)\left] {_{ 2} } \right[{\text{Cu}}^{\text{II}} \left( {\text{en}} \right)_{ 2} } \right]_{ 2} } \right\}^{ 2- } . The compound 2 consists of protonated L ligand and [SiW₁₂O₄₀]⁴⁻ anion. The protonated L ligands have been extended into a 2D network via hydrogen-bonding interactions. The guest [SiW₁₂O₄₀]⁴⁻ clusters have been incorporated into the square voids of the 2D host network as templates. The electrochemical behavior and electrocatalysis of compound 2 bulk-modified carbon paste electrode (2-CPE) have been studied.     

Electro-Catalytic Oxidation of Methanol on a Ni–Cu Alloy in Alkaline Medium

The electro-catalytic oxidation of methanol on a Ni–Cu alloy (NCA) with atomic ratio of 60/40 having previously undergone 50 potential sweep cycles in the range 0–600 mV vs. (Ag/AgCl) in 1 m NaOH was studied by cyclic voltammetry (CV), chronoamperometry (CA) and impedance spectroscopy (EIS). The electro-oxidation was observed as large anodic peaks both in the anodic and early stages of the cathodic direction of potential sweep around 420 mV vs. (Ag/AgCl). The electro-catalytic surface was at least an order of magnitude superior to a pure nickel electrode for methanol oxidation. The diffusion coefficient and apparent rate constant of methanol oxidation were found to be 2.16 × 10⁻⁴ cm² s⁻¹ and 1979.01 cm³ mol⁻¹ s⁻¹, respectively. EIS studies were employed to unveil the charge transfer rate as well as the electrical characteristics of the catalytic surface. For the electrochemical oxidation of methanol at 5.0 m concentration, charge transfer resistance of nearly 111 Ω was obtained while the resistance of the electro-catalyst layer was ca. 329 Ω.     

Investigation of N<Subscript>2</Subscript>-fixation on polyaniline electrodes in methanol by electrochemical impedance spectroscopy

The ac response of polyaniline thin films on platinum electrodes was measured at different dc potentials during the N₂-fixation in methanol + LiClO₄ electrolyte with 0.03 mol L⁻¹ H₂SO₄ for the first time. The optimum film thickness was found to be 1.5 μm, N₂-pressure 50 bar and an optimum electrolysis potential of −0.12 V (NHE). The diffusion coefficients for N₂ into the polymer film was found to be (5 ± 2)×10⁻⁹ cm² s⁻¹.     

Determination of cadmium (II) using H<Subscript>2</Subscript>O<Subscript>2</Subscript>-oxidized activated carbon modified electrode

Pristine activated carbon (AcC) was oxidized by H₂O₂ under ultrasonic conditions. Compared with pristine AcC, the H₂O₂-oxidized AC possesses higher accumulation ability to trace levels of Cd²⁺. Based on this, a highly sensitive, simple and rapid electrochemical method was developed for the determination of Cd²⁺. In 0.01 mol L⁻¹ HClO₄ solution, Cd²⁺ was effectively accumulated at the surface of H₂O₂-oxidized AcC modified paste electrode, and then reduced to Cd under −1.10 V. During the following potential sweep from −1.10 to −0.50 V, reduced Cd was oxidized and a sensitive stripping peak appears at −0.77 V. The stripping peak current of Cd²⁺ changes linearly with concentration over the range 5.0 × 10⁻⁸ to 5.0 × 10⁻⁶ mol L⁻¹. The limit of detection was found to be 3.0 × 10⁻⁸ mol L⁻¹ for 2-min accumulation. Finally, this new sensing method was successfully used to detect Cd²⁺ in waste water samples.     

Water vapor and oxygen permeability of wax films

The water vapor (WVP) and oxygen (O₂P) permeabilities of beeswax (BW), candelilla wax (CnW), carnauba wax (CrW) and microcrystalline wax (MW), formed as freestanding films, were determined. CnW and CrW both had small values for O₂P (0.29 and 0.26 g·m⁻¹·sec⁻¹·Pa⁻¹ × 10⁻¹⁴, respectively), which are less than half the value for high-density polyethylene and about a decade greater than the value for polyethylene terephthalate. O₂P values for BW and MW were about 6−9× greater than those of CnW and CrW. WVP of CnW was 0.18 g·m⁻¹·sec⁻¹·Pa⁻¹ × 10⁻¹², which is about one-half the value for CrW and MW and about one-third the value for BW. The WVP of CnW was somewhat less than that of polypropylene and somewhat greater than that of high-density polyethylene. Differences in permeabilities among the wax films are attributed mainly to differences in chemical composition and crystal type as determined by X-ray diffraction.     

Chelating ionophores based electrochemical sensor for Hg(II) ions

Poly(vinyl chloride) (PVC)-based membranes of pyrimidines, 1-(2′-aminoaryl)-4, 4, 6-trimethyl-1, 4, 5, 6-tetrahydro-6-hydroxypyrimidine-2-thiol (HPT) (R = −H, −CH₃, −OCH₃) with sodium tetraphenylborate (NaTPB) as an anion inhibitor and dibutylphthalate (DBP), dioctylphthalate (DOP), dibutyl (butyl) phosphonate (DBBP) and 1-chloro naphthalene (CN) as plasticizing solvent mediators were prepared and used as Hg²⁺ selective electrodes. Optimum performance was observed with the membrane having HPT(−OCH₃)−PVC−NaTPB−DOP in the ratio 1:33:1:65 (w/w). The electrode works well over a wide concentration range 5.0 × 10⁻⁶−1.0 × 10⁻¹ M (detection limit 1.0 ppm) with Nernstian compliance (29.5 mV decade⁻¹) between pH 2.5 and 4.0 with a fast response time of about 20 s. The selectivity coefficient values of the order of 0.001 for mono-, bi- and trivalent cations, indicate high selectivity for Hg²⁺ ions over these cations. Further, anions such as Cl⁻ and SO ₄ ²⁻ do not interfere in the functioning of Hg²⁺ sensor. The electrodes were used over a period of five months with good reproducibility (std. dev. ±0.2 mV) and the performance of the electrodes was found satisfactory even up to 10% nonaqueous medium. The electrode assembly was also evaluated for potentiometric determination of Hg²⁺.     

Characterization of MgMnxFe2?xO4 as a possible cathode material for electrochemical reduction of NOx

Spinel-type oxides of MgMn _x Fe_2−x O₄, x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, were synthesized as a solid state reaction and characterized with dilatometry and resistivity measurements up to 1000 °C. Results showed a general decrease of the linear expansion and an increase in conductivity as a function of the Mn content. Point electrodes were analyzed from 300 to 600 °C in a pseudo-three-electrode setup in 1% NO, 1% NO₂, and 10% O₂ using cyclic voltammetry. The activities in O₂ were in general very low whereas the activities in NO were slightly higher. The activities in NO₂ were for all materials much higher than the activities in O₂. Even though Mn tends to decrease the activity of the materials, current ratios of I_NOx/I_O2I_{{\rm NO}_{x}}/I_{{\rm O}_2} have relatively high values in both NO and NO₂.     

Differential pulse voltammetric determination of chlorphenoxamine hydrochloride and its pharmaceutical preparations using platinum and glassy carbon electrodes

Voltammetric methods have been used for the determination of chlorphenoxamine hydrochloride (Ch-HCl) in raw material and in its pharmaceutical preparations (Allergex and Allergex caffeine tablet). It was found that Ch-HCl gives a characteristic cyclic voltammetric (CV) and differential pulse voltammetric (DPV) peak in acetonitrile using platinum and glassy carbon working electrodes. The I _p of the DPV peak increases linearly within the concentration range from 4.5 × 10⁻⁴ to 1.0 × 10⁻² mol L⁻¹ of the investigated drug. The concentration of Ch-HCl in raw drug material and in its pharmaceutical preparations was determined using the standard addition method, Randles–Sevcik equation and indirectly via its complexation with sodium tetraphenylborate (NaTPB). The obtained over all average recoveries were 101.44 and 100.49% with SD 0.45 and 0.38 (n = 4) for platinum and glassy carbon electrodes, respectively. The effect of scan rate, sample concentration, and supporting electrolyte on the I _p and E _p was also investigated.     

Lack of increased availability of root-derived C may explain the low N2O emission from low N-urine patches

Urine deposition on grassland causes significant N₂O losses, which in some cases may result from increased denitrification stimulated by labile compounds released from scorched plant roots. Two 12-day experiments were conducted in ¹³C- labelled grassland monoliths to investigate the link between N₂O production and carbon mineralization following application of low rates of urine-N. Measurements of N₂O and CO₂ emissions from the monoliths as well as C signal of evolved CO₂ were done on day −4, −1, 0, 1, 2, 4, 5, 6 and 7 after application of urine corresponding to 3.1 and 5.5 g N m⁻² in the first and second experiment, respectively. The C signal was also determined for soil organic matter, dissolved organic C and CO₂ evolved by microbial respiration. In addition, denitrifying enzyme activity (DEA) and nitrifying enzyme activity (NEA) were measured on day −1, 2 and 7 after the first urine application event. Urine did not affect DEA, whereas NEA was enhanced 2 days after urine application. In the first experiment, urine had no significant effect on the N₂O flux, which was generally low (−8 to g N₂O-N m⁻² h⁻¹). After the second application event, the N₂O emission increased significantly to g N₂O-N m⁻² h⁻¹ and the N₂O emission factor for the added urine-N was 0.18%. However, the associated ¹³C signal of soil respiration was unaffected by urine. Consequently, the increased N₂O emission from the simulated low N-urine patches was not caused by enhanced denitrification stimulated by labile compounds released from scorched plant roots.     

Electroreduction of molecular oxygen on preferentially oriented platinum electrodes in acid solution

The oxygen electroreduction reaction was studied on two different preferentially oriented ((111)-type and (100)-type and on a conventional polycrystalline (PC) platinum rotating disc electrodes in acid solutions at 30 °C. At low overpotentials, Tafel lines of –0.060 V decade^–1 were obtained on the three electrodes in oxygen-saturated 1.0m H₂SO₄ and 1.0m H₂SO₄ + y m K₂SO₄ (0 y 1). At high over-potentials the usual Tafel slope of -0.120V decade^–1 was observed on both (111)-type and PC platinum electrodes in 1.0m H₂SO₄, whereas a slope of –0.165V decade^–1 was found on (100)-type platinum. In oxygen-saturated 1.0m H₂SO₄ the surface coverage by O-containing adsorbates on (100)-type platinum was greater than on both (111)-type and PC platinum. Rotating ring-disc electrode data showed that a higher amount of H₂O₂ was produced on (100)-type platinum than on the other platinum surfaces. The overpotential against current density plots are influenced by the anion concentration depending on the type of preferentially oriented platinum.